Hi Dale (@DaleKramer)!
This is not Asad speaking in the video but my colleague Milad (@Milad_Mafi) - just to make that clear
The “shape” of the velocity profile really depends on which state you are talking about. Turbulent flows usually have a velocity profile that have a higher gradient at the wall due to increased momentum transport.
On the left side you see a laminar velocity profile and on the right side a turbulent velocity profile for Poiseuille flow. Another assumption that is made when drawing these profiles is that we actually look at the “mean” because in fact there is a fluctuating velocity field instantaneously which looks a bit chaotic as depicted below.
This becomes important when talking about Reynolds Averaging but that’s another topic.
Separation (same case for airfoils) requires an adverse pressure gradient to change the direction of the slow fluid to the other direction (roughly speaking). On a flat plate we assume constant pressure gradient thus no adverse pressure gradient.
P.S.: Actually good material to talk about - maybe I will do a video about such stuff in the future (if even necessary)
Also keep in mind that Boundary Layer theory is nothing easy - just have a look at the book from Hermann Schlichting about Boundary Layer theory, have fun
Picture 2: Turbulence Modeling for CFD by David C. Wilcox